ANNUAL FLUCTUATIONS ZOOPLANKTON IN IN BIOMASS OF TAXONOMIC GROUPS

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					ANNUAL FLUCTUATIONS IN BIOMASS OF TAXONOMIC GROUPS OF
      ZOOPLANKTON IN THE CALIFORNIA CURRENT, 1955-59

                                                      J. M.COLEBROOKl

                                                          ABSTRACT
                                                                                                                                        @

               Year-to-year fluctuations in the abundance of the zooplankton of the California Current region, from
               1955 to 1959, have been studied. The abundance of zooplankton was measured in terms of the biomass
               of each of 17 major taxonomic categories (generallyClass or Order). Principal components analysis was
               used to produce concise descriptions of the major elements of the fluctuations in the abundance of the
               categories in each of 14 areal subdivisions of the survey area. Considerable coherence with respect tn
               annual changes was found both between the taxonomic categories and between the areas. The
               principal common element in the fluctuations could be associated with a marked increase in the
               temperature of the surface waters which occurred in 1957 and persisted through 1958 and 1959. A less
               pronounced but still quite clear common element in the fluctuations could be associated with year-to-
               year fluctuations in the amount of coastal upwelling in the area.


Since 1949, the regular surveys conducted by the                    available from the survey data in order to discover
California Cooperative Oceanic Fisheries Inves-                     whether observed changes can be associated with
tigation (CalCOFI, program have yielded infor-                      environmental fluctuations.
mation about a variety of physical, chemical, and
biological parameters (see, e.g., Marine Research                                          MATERIAL
Committee 1957). For the CalCOFI survey cruises
during January, April, July, and October for each                      The details of t h e procedures for deriving
of t h e y e a r s from 1955 to 1959, samples of                    biomass estimates have been described by Isaacs
zooplankton were analyzed to provide estimates of                   et al. (1969). who also give the reasons for the
the biomass for each major taxonomic category                       selection of the particular set of taxa (listed in
within the zooplankton tIsaacs et al. 1969).                        T a b l e 1). I t was t h e i r i n t e n t i o n to provide
    These data were generously made available to
the author by J . D. Isaacs to provide material for a
study of year-to-year changes in the abundance of                   T:\l{l.b: 1.-A  list of the taxa from CkCOFI cruises for which
                                                                    biomass estimates arcs available. They are listed in alphabetical
t h e major components of the zooplankton. As                       order and a code used in Figures 7 and 10 is given.
stated by Isaacs et al. t1969), “Selection of the                   ._                                  ~-         __
                                                                        Taxa      -         C O T 7            Taxa            Code.
                                                                                                                                   -
years 1955 through 1959 for analysis of biomass                     Amphipoda               AMPH           Larvacea            LARV
distribution was dictated by interest in t h e                      Chaetognatha            CHET           Medusae             MEDS
                                                                    Cladocera               CLAD           Mysldacea           MYSD
occurrence and nature of patterns of seasonal and                   Copepoda                COPD           Ostraccda           OSTR
annual variability among the functional groups of                   Crustacea larvae        CRST           Pteropoda           PTER
                                                                    Ctenophora              CTEN           Radiolaria          RADL
zooplankton. During t h i s time, yearly mean                       Decapoda                DECP           Siphomphora         sipti
temperatures above the thermocline shifted up-                      Euphausiacea            EUPH           Thaliacea           THAL
                                                                    Heteropoda-             HETP                          - __
ward from the relatively cold years of 1955 and                                                             ~    ~~




1956 to the relatively warm years of 1958 and
 1959.”                                                             estimates of the “nutrient quality” of the standing
    The object of the study described in this paper is             .crop of zooplankton a s well a s a n index of
to describe the annual changes, from 1955 to 1959,                  “trophodynamic complexity.” The categories were
in t h e abundance of t h e zooplankton of t h e                    chosen to represent the quality and quantity of
CalCOFI survey area in as much detail as is                         zooplankton as food for fish r a t h e r t h a n a s
                                                                    indicators of variability of the zooplankton as
                                                                    such.
  ‘Institute for Marine Environmental Research, Plymouth,
                                                                       T h e collection method for t h e s t a n d a r d
England.                                                            CalCOFI plankton samples has heen described in
Manuscript nccepted Octoher 1976.                                                                                               357
FISHERY ULII.I,I?TIN. VOL. 75. NO 2. 1977
                                                                                   I
                                                                                   $35.




                                                                             -
detail by, e.g., Ahlstrom (1954) a n d Fleminger
(1964). Very briefly, the net is 1 m in diameter at
t h e m o u t h a n d 5 m long, the filtering section
having a mesh size of about 0.5 mni. T h e net is
                                                                                 I INSHORE
towed obliquely, from a ship traveling at a speed of                             2 OFFSHORE
about 2 knots, from t h e surface down to a depth of.                            3 SEAWARD

140 m a n d t h e n r e t u r n e d to t h e surface. T h e
volume of water fitercd varies from about 400 to
600 m'.
    C h a r t s of t h e distribution of biomass for each                    v
                                                                              * 4 INSNSHORE
taxon have been given by Isaacs e t al. (1969) for                            0 5 OFFSHORE
                                                                                6 SEAWARD
t h e April a n d October cruises. by Isaacs e t al.
( 1 9 7 1 ) for t h e J a n u a r y cruises, a n d by Fleminger
et al. (1974)for t h e July cruises. T h e station d a t a
a r e held on ;I magnetic (ape file a t t h e Southwest
F i s h r 1. i e s ('enter . N I t i on a I M D r i n e F i s h e r i e s
S e w ice.
                                                                             - 7 INSWE
                                                                             * 8 OFFSHORE
                                                                               9 SEAWARD
                                                                               O
                                                                              I EXTENDED

        DATA PROCESSING METHOI)S

    For t h e purposes of presenting s u m m a r i e s of                    *I I INSHORE
                                                                             *I2 BAY
CalCOFI d a t a in a compact form a n d to permit                              1 OFFSHORE
                                                                                3
                                                                             *  4
                                                                               1 SEAWARD
some smoothing of t h e d a t a by t a k i n g average                          5
                                                                               1 EXTENDED
values, P. E . Smith's proposal for subdividing t h e
survey a r e a into 2 3 zones was used in t h i s study
( F i g u r e 1). T h e extent of t h e survey a n d hence t h e             smJliW4
                                                                                6
                                                                               1 INSHORE
number of stations occupied varied from cruise to                            *I7 OFFSHORE
                                                                             *I8 SEAWARD
c r u i s e . T h e s t a t i o n p a t t e r n s for t h e c r u i s e s      1 EXTENDED
                                                                                9

included in t h i s study are given in S m i t h ( 1971 1,
a n d a s u m m a r y showing t h e numbers of samples
in each zone is given in Table 2.                                           .-
                                                                             *2D   INSHORE
    T h e biomass d a t a are available as grams!l,000                        2I
                                                                              22
                                                                                   CfFSHDRE
                                                                                   SEAWARD
m:I a n d estimated to two decimal places. T h e r a n g e                    23   EXTENDED

of estimates is from zero to over 5.000 g , a n d
within each taxon they are heavily positively
skewed.
                                                                            PI(;( ttk: 1 .-A chart of the area of the C'iiICOFI survey showing
    T h e results presented here were expressed in
                                                                            the grid of station positions on which were hased the cruises
t e r m s of relative changes in biomass in time a n d                      during the period 1955-59. Also shown IS the subdivision of the
space within each taxonomic category, a n d exten-                          :ires into the standard zones used in this study. The well-

sive a v e r a g i n g w a s employed. I t w a s decided,                   sainpled zones for which annual means of biomass were calcu-
therefore, to apply a logarithmic transformation                            lated iirr marked with an asterisk (see Table 21.
to t h e original estimates. Averages based on log
transformed values a r e weighted in favor of t h e                         involving t h e calculation of m e a n s for each zone
more numerous low values as opposed to a r i t h -                          for each cruise for a s u b s e t of t h e taxonomic
m e t i c m e a n s , t h e v a l u e s of w h i c h m a y b e              categories indicated t h a t adding 1.O produced a
determined largely by small n u m b e r s of high                           considerable loss of resolution for m e a n s corre-
estimates.                                                                  sponding to less t h a n 1 gi1,OOO m3, a n d adding
    In order to give zero a value on t h e transfotmed                      0.01 produced a resolu'tion of low m e a n s t h a t ap-
scale it is normal to add 1 t o t h e observation prior                     peared to be greater t h a n w a s warranted by t h e
to transformation. I n t h i s case, where t h t I)lomass  I   '            accuracy of the d a t a . Therefore throughout this
h a s been e s t i m a t e d to two decimal places, a                       study a transformation of t h e form
number of options is available, either 1.0, 0.1, or
0.01 can be added prior to transformation. Trials                                              Y   =   log,,,   (lox +   1)
358
COLEBROOK FLUCTUATIONS IN BIOMASS OF ZOOPLANKTON

TABLE 2.-The n u m b e r s of samples collected during each o f t h e J a n u a r y (Jn),April (Ap), July ( J l ) , a n d October (Oc)CalCOFI cruises
for t h e years 1955-59 in each o f t h e s t a n d a r d zones (see F i g u r e 1 ), A n n u a l t o t a l s a r e g i v e n in boldface and t h e g r a n d t o t a l is printed in
italic.

                                     1955                        1956                          1957                         1958             -___1959
                                                TO-                 To-                         To-                                TO-                           To-           Grand
          Zone             Jn Ap      JI Oc tal         Jn Ap JI Oc tal             Jn Ap JI Oc tal               Jn Ap      JI Oc tal         Jn Ap     JI   Oc tal            total
Central California
    Inshore                 0    0 13 13 26              0 18 16        0 34          0    0 16       0 16         9 2 23 20 73
                                                                                                                      1                        15 20 24 18 77                   226
    Offshore                0    0    9     6 15         0 9 18         0 27          0    0 10       0 10         2 2 20 17 60
                                                                                                                      1                        12 14 30 18 74                   186
Southern California
    Inshore                20 17 27 22 86                1
                                                        2 22 29 27 99                 0 25 26 26 77               18 27 26 29 100             29 28 28 27 112                   474
    Offshore                4 6 14 6 30                  4 6 13 9 32                  0 7 12 6 25                   5 13 14 9 41                6 12 14 9 4 1                   169
    Seaward                 3 17 20 6 46                 5 13 26 6 55                 0 17 23 17 57                    1
                                                                                                                  I 1 2 27 17 76              1 1 30 29 17 87                   321
Baja California
    Inshore                12   12   1 12 50
                                      3                 12 12 14        0 38          8   13   12     13 46       12   13         3
                                                                                                                             1 1 1 49          13   14   13   14   54           237
    Bay                    12   13   14 1 1 50          11 12 15        0 38         12   15   16     14 57       10   16    14 16 56          15   16   17   16   64           265
    Offshore               11   13   26 4 54            11 1 1 22       0 44         10   20   26     1 1 67      10   25    25 18 78          18   26   24   16   87           330
    Seaward                 4   12   24 5 45                 6
                                                         6 1 20         0 42          2   16   19     13 50       10   30    23 18 81          18   29   29   18   94           312
South Baja
    Inshore                16 15 1 14 61
                                  6                     13 13 14        0 40         16 15 17 17 65               15 16 17 17 65               17 1 1 19 17 64                  295
    Offshore                8 12 13 6 39                 8 8 13         0 29          8 2 18 12 59
                                                                                         1                        12 22 19 20 73               19 17 27 20 83                   283
    Seaward                 3 2 2 310                    1 2 2          0 5           112131339                    315 6 731                    8 712 835                       120
Cape
    Inshore                15    0    0     0 15        16 16      0    0 32          0 19      0     0 19        17    0     0 17 34         20 10       0    0 30             130
    Offshore                1    0    0     0    1       110       0    011           022       0     022         10    0     02434           3 14
                                                                                                                                               1          0    045              113
                                                                                                                                                                           ~




h a s been employed. By t h i s transformation,                                                were calculated for each taxon for each of a set of
means corresponding to greater than about 0.2                                                  regularly sampled zones (those marked with an
gi1,OOO m3 are virtually on a logarithmic scale                                                asterisk in Figure 1); and principal components
while lower means show a progressive transition                                                analysis was used to extract from these data the
to a n arithmetic scale.                                                                       main patterns of year-to-year change in biomass.
   Quarterly means were calculated by averaging                                                This is a technique of multivariate analysis (see,
the data for the stations in each zone and then                                                e.g., Kendall 1957) which generates a sequence of
these were averaged to give annual values. For                                                 variables known as components with, in this case,
those occasions when less t h a n five stations were                                           values for each year, which are the weighted sums
occupied in a n y zone, t h e station d a t a were                                             of the standardized data variables, in this case
ignored and a quarterly mean was interpolated by                                               sets of annual means of the taxonomic categories.
the following method:                                                                          The sets of weighting factors, with values for each
                                                                                               taxonomic category, a r e the successive latent
1. For each taxonomic category the set of overall                                              vectors of the correlation matrix derived from the
   zone means ( t h e sum of all the observations                                              original data, in this case the table of correlations
   for all the cruises in each zone divided by the                                             between the annual variations in abundance of all
   total number of stations occupied in the zone)                                              possible pairs of taxonomic categories. The first
   was calculated. The set of overall quarterly                                                latent vector generates a component which has
   means ( t h e sum of all the observations for all                                           the largest possible variance. The second vector
   the cruises in each quarter divided by the                                                  generates a component which has the largest
   number of stations in each q u a r t e r ) was                                              possible variance in relation to t h e residual
   calculated.                                                                                 following the removal of the variability associated
2. For e a c h m i s s i n g v a l u e t h e s u m of t h e                                    with the first component, and so on. If the original
   remaining means for the other zones for the                                                 data are coherent to any extent, it is normal for
   cruise a n d t h e s u m of t h e corresponding                                             the first few components to account for a large
   overall zone means were calculated. T h e                                                   proportion of the variability of the original data
   l a t t e r was weighted by t h e r a t i o of t h e                                        array.
   relevant overall quarterly mean to the grand
   mean and the missing value then calculated                                                         GEOGKAPHICAL DlSTRlBUTlONS
   as the product of the remaining zone means
   for the cruise and the weighted sum of the                                                    To provide some geographical background t o
   overall zone means.                                                                         the study of year-to-year changes in biomass,
                                                                                               charts of the overall mean for each taxon in each
   From these quarterly means, annual means                                                    standard zone were prepared. In order to search
                                                                                                                                                                               359
                                                                                                    FISHERY BU1.I.ETIN. VOL 75. NO. 2

                                                                        FIRST COMPONENT         SECOND COMPONENT
for possible relationships between the geograph-
ical distributions of t h e taxonomic categories,
these data were subjected to a principal compo-
nents analysis.
   Figure 2 is a graph of the first latent vector
plotted against t h e second. The graph has a point
for each taxonomic category, and the disposition of
points represents in a spatial form the relation-
ships between the geographical distributions of
the taxonomic categories with respect to the first
two components which, in this case, account for
61% of the variability of the original geographical
distributions. The interrelationships a r e probably
best regarded in the form of a more or less circular
sequence; only the point for Medusae falls well off
the sequence.                                                           FI(;I’RI.: 3.-Charts of the first and second components derived
   Figure 3 shows charts of the first two compo-                        from a principal components analysis of the geographical dis-
nents. The first component shows a very clear                           tributions of the taxa.
north to south, alongshore gradient; and t h e
second shows a n equally clear inshore to offshore
gradient, indicating that the sequence of cate-                         distributions of t h e taxonomic categories a r -
gories in Figure 2 runs from categories with                            ranged in this sequence. They a r e based on
northern distributions (Siphonophora to Radio-                          averages of the transformed data, for each zone,
laria) to inshore distributions (Euphausiacea to                        for each quarterly cruise for the period 1955-59,
Cladocera) to southern and inshore distributions                        excluding zones for which fewer than five stations
(Larvacea to Mysidacea) to offshore distributions                       were occupied. These distributions show varia-
(Heteropoda to Ostracoda). Figure 4 shows the                           bility other than that involved in their relation-
                                                                        ships with the first two components; nevertheless,
                                                                        the north to inshore to south to offshore sequence
                                                                        c a n be seen fairly clearly. Heteropods a n d
               (ONSHORE)       t05*                                     Pteropods are firmly placed in the sequence of
                                           CRST                         taxonomic categories in the vector plot in Figure
                               t O 4 - - .CHET    .COP0                 2. They have, however, fairly low values compared
                        CLAD.                           EUPH
                                                                        with the other categories, and only parts of their
                               tO3--                                    distributions conform with the south to offshore
              LARV.                                                     transition indicated by their position in the vector
            DECP.              t02--                                    plot. The distribution of Medusae (Figure 4)can be
                                                                        seen to include areas of relatively high biomass
         MYSO.
                                tot--                      (NORTH)      both in the north and in the south, and clearly it
  (SOUTH)                                                      RADL
-04    -03       -02     -01             +01      to2     to3
                                                                        does not fit i n t o t h e sequence of t h e o t h e r
  I                                                        ‘AMpHQ “1    categories.
                                                               CTEN
                                                                            It is obviously unrealistic to attempt to classify
                       HETP.       __                       THAL.       the internally diverse taxonomic categories used
                        PTER                                    *SIPH   here in terms of geographical distribution types
                                                                        such as Brinton (1962) found for Euphausincen.
                                                                        Brinton found that the alongshore axis of the
                                                                        California Current in the CalCOFI survey area
                                                                         was characterized by transitions from “subarctic”
              (OFFSHORE)       -04l                                     species in the north to “transition” species in the
                                                                        region between lat. 30” and 40”N to “equatorial”
FIGURE   2.-A plot of the first vector against the second vector
derived from a principal components analysis of the geographi-          species in the south. “Central” species occurred
cal distributions of the taxa. A key to the abbreviations of the        offshore and some “boundary” species occurred
names of the categories is given in Table 1 .                           inshore in the area. McGowan (1971) has shown
360
C01,EBHOOK FLUCTUATIONS I N BIOSIASS OF Z 0 0 P l A S l i T O S

t h a t these patterns a r e reflected generally in t h e                    zones on t h e a n n u a l fluctuations i n biomass of
distribution of t h e plankton of t h e Pacific Ocean.                       each taxonomic category a n d secondly for each
I t m a y , n e v e r t h e l e s s , be significant t h a t t h e           taxonomic category on t h e a n n u a l fluctuations in
pattern of distribution o f t h e taxonomic categories                       abundance in each of t h e s t a n d a r d zones. T h e
reflects both t h e alongshore a n d t h e inshore-                          s a m e d a t a a r e involved in both sets of antilyses.
offshore transitions i n t h e distribution of t h e                             Graphs of t h e first principal components for
Euphausiacea.                                                                each of t h e zone analyses a r e given in F i g u r e 5.
                                                                             Table 3 shows t h a t these components accounted
      YEAR-TO-YEAR FLUCTUATIONS                                              for between j u s t under one-half a n d about three-
              IN BIOMASS                                                     q u a r t e r s of t h e total variability; it also shows t h a t
                                                                             all but n very few o f t h e categories showed positive
  Annual means of biomass were calculated. as                                relationships with t h e components. T h e graphs
described above, for each taxonomic category                                 show considerable similarity between t h e various
(Table 1) for each of t h e well-sampled standard                            zones. These results indicate t h a t a large element
zones ( F i g u r e 1)for each of t h e years 1955-59.Two                    of t h e y e a r - t o - y e a r fluctuation in b i o m a s s is
sets of p r i n c i p a l c o m p o n e n t s a n a l y s e s w e r e        common to all t h e zones a n d to a vast majority of'
carried out, firstly for each of t h e 14 standard                           t h e taxonomic categories. Nearly a l l t h e zotws
                                                                             show a relatively high biomass irelative t o a mean
TABLE3.-For each zone i n ) the percentage of the total variabil-            of zcro) in 1955 a n d 1956 a n d a low biomass in
ity of the original d a t a accounted for by the first component a n d       1958 a n d 1959. T h c d a t a for 1957 vary from zone
tb) t h e number of taxa with positive first vector values (mal;-            to zone, p e r h a p s t e n d i n g to b e h i g h e r in t h e
imum = 17).The code names for the zones used in Table 4 and
Figures 6 and 9 a r e also given.
                                                                             northern a n d offshore zones a n d lower in some of
                                                                             t h e southern and inshore zones.
         Zone                                a
                                  Code ___._____-                     b
Central California.
                                                                                 A t a b l e w a s p r e p a r e d of t h e corresponding
    Inshore                     CCALIN               74               17     vectors with t h e taxonomic categories arranged.
    Onshore                     CCALOF               71               17
Southern California                                                          by trial and error, to give t h e high positive t e r m s
    Inshore                     SCALIN               63               14     a t t h e top, a n d t h e low positive a n d t h e few
    Offshore                    SCALOF               58               17
    Seaward                     SCALSW               58               15     negative t e r m s a t t h e bottom of t h e table. T h e
Bala Calilornia                                                              final r a n k i n g of' categories a n d t h e vector values
    Inshore                     BCALIN               70               15
    Bay                         BCALBY               66               16     a r e given in Table 4. This r a n k was compared \vith
    Offshore                    BCALOF               52               14
                                                                             t h e r a n k of t a x a bt1st.d on t h e r e l a t i o n s h i p s
    Seaward                     BCALSW               48               13
South Bala:                                                                  between their geographical distributions ( F i g u r e
     Inshore                    SBAJIN                 64             16
    Offshore                    SBAJOF                 56             16
                                                                             2, stai.ting with t h e noitherti distributions, with
     Seaward                    SBAJSW                 45             12     Siphonophora a n d Thaliacea, working round t h e
Cape'
     Inshore                    CAPEIN                 54             15     sequence a n d ignoring Medusae (also left out of
     Offshore                   CAPEOF                 53
                                                    ___.__
                                                                      16     Table 4)to finish with Pteropoda a n d Ostracoda.


TAIILI.: 4.-The    first vectors of principal component analyses for each standard zone with the taxonomic categories ranked a s described
                                       in t h e text. Also t h e rank of the catrgorws derived from Figure 2 .
~~_______~-                                                                                      - _ ~ _ _ _ . _ _ ~ _ _.~



    Taxa
Copepoda                 0 28      0 28   0 30   031        036     0 29   0 29   030     034     030     0 30   031     027     030         7
Thaliacea                0 27      0 27   030    028        031     0 28   029    032     033     029     0 31   029     030     031         2
Arnphipoda               0 27      0 28   030    032        031     0 27   028    031     033     028     0 28   0 22   029    028           4
Siphonophora             0 27      0 28   022    029        023     0 29   0 29   025     0 29    0 28    0 30   032    028   028            1
Radiolaria               0 28      0 27   030    029        031     0 28   028    0 30    0 28    023     0 28   020     02    000           5
Ctenophora               0 26      0 27   030    026        028     0 26   026    026     033     027     0 26   006    016    005           3
Decapoda                 0 25      0 25   026    029        029     0 27   024    031     029     024     0 28   029    030    033          12
Euphausiacea             0 27      0 26   028    026        026     0 28   021    014     017     024     0 28   018    018    031           6
Chaefognafha             0 28      0 27   030    028        028     0 27   024    011     027     024     0 25    26    031    032           9
Crustacea larvae         0 25      0 06   030    027        022     0 25   024    017      09     025     0 31    25    029    011           8
Heleropoda               0 15      0 24   014    018        023     0 16   029    020     007     0 19    0 29   0 1 9 0 2 7 0 2 8          14
Larvacea                 0 28      0 27   017    013        024     0 27   029    021      05     022       08   029    022    023          11
Ostracoda                0 22      0 26    01    026        023     0 12   018     023    013     018     0 11    21    021    024          16
Cladocera                0 12      0 19    03    001        003       23   003      25    006     023     0 17   011    009     08          10
Pleropoda                0 19      0 13   010    008         02     0 04   012      02     19      06     005     08     17    021          15
Mysidacea
_  .                     0   15    0 17    28    009         15     0
                                                                  ___ 08   0 _
                                                                           _1 1   ~ 12 _ _ _ _ _ ~2 6
                                                                                  -__      27    0
                                                                                                          -~ 33
                                                                                                          014            0 2 9 0 1 6        13


                                                                                                                                          361
                                                                                                   FISHERY BULLETIN: VOL. 73. NO 2

                 SIPHONOPHORA           THALIACEA               CTENOPHORA             AMPHIPODA




                FI(;t'I<K4.-Charts of the geographical distribution ofbioinnss for each ofthr taxa based on Iiiparithmic means for
                each standard zone I see Figure 1I for all the C'alCOFI cruises for 1955-59. Contours a r e drawn tit levels correspond-



The ranks are given in Table 4, and the value of                    features of t h i s pattern with only Cladocera
Spearman's rank correlation coefficient between                     showing a negative relationship.
the two ranks i s + 0.806 which is significant a t the                These results suggest that whatever influence
0.1% level.                                                         or influences are responsible for the fluctuations
  Figure 6 shows graphs of the first principal                      in the plankton either have their origin in the
components of the analyses for each taxonomic                       north of the survey area or have a greater effect on
category with the categories ranked in the same                     those categories with northern patterns of distri-
order as in Table 4. All the northern and inshore                   bution. It is, a t least, fairly safe to infer that there
categories, down to Crustacea larvae in Figure 2,                   is some commonality between t h e influences
show the same form of year-to-year fluctuations in                  which determine geographical distribution and
biomass as do the zones, with relatively high                       those which are responsible for the form of the
biomass in 1955 and 1956 and low biomass in 1958                    year-to-year changes in biomass.
and 1959. The remaining categories show some                          The years from 1955 to 1959 were deliberately
362
ing to the mean + 1 SD, the mean, and the mean - 1 SD. The keys to the contour levels for each category give the arithmetic values, as
grams per 1,000 m*, corresponding to these levels.



chosen for the production of biomass data to cover                   Figure 7 . Favorite and McLain (1973) showed that
a period of marked change in physical conditions                     this is part of a widespread change in surface
and in the distribution of many species in the                       temperature affecting almost the whole of the
CalCOFI area. The main features of these changes                     North Pacific Ocean. The reasons for the change
have been described in the proceedings of a special                  are not yet completely clear. The initial warming
symposium (Sette and Isaacs 1960). The most                          in 1957 appears to be associated with a reduction
striking feature was a considerable warming of                       in the flow of the California Current which
the surface waters which started in the south in                     occurred between the late summer of 1957 and
1956 and spread through the area during 1957                         midsummer 1958. As an index of the flow of the
(see, e.g., Longhurst 1967).                                         California Current, Saur (1972) used the differ-
   The general form of the change can be typified                    ence in sea level between Honolulu and San
by the variation in temperature in the top 50 m in                   Francisco. A plot of monthly means (with a linear
the southern California offshore area shown in                       trend removed and adjusted to normal atmo-
                                                                                                                                 363
                                                                                                       FISHERY BULLETIN: VOL. 75, NO. 2




                -2
                -4
                -6
                                                                                               CTEN




-2
-4
-6
                                                                                             P+ R:
0
                                                                      -2
-2
                                                                      -4
-4
-6                   U             U               U




-2
-4
-6                                 U                                  -6"                    U         U          U
                                                                                             555657585955565758595556575859
                                                                      t6,      MEDS




                -2
                -4
                                   U
                                                                      K
                                                                      P
                                                                      -2
                                                                      - 4
                                                                      -6,
                -6                                                          55 56 57 58 59                YEAR
                     555657 5859 55565758 59
                                                                      F I ( , II<E (<.-Graphs li)r each taxon of the first principal compo-
                               YEAR
                                                                      nc.nt of the year-to-year fluctuations in biomass for all the well-
                                                                      winpled ('aICOFI standard zones. A key to the abbreviations o f
FI(;CHE 5.-Graphs for each of the well-sampled CalCOFI zones
                                                                      1 1 1 0 namt's o f t h e taxa is given in Table 1. They a r e in the same
(see Figure 11 of the first principal component of the year-to-year
                                                                      (ii.dcr iis iii Table 1 see text). Each graph has a mean ofzero and
fluctuations in biomass of all the 17 taxa. Each graph IS druwn
                                                                      the, \,crtic;iI sc;ile is in SD units
with a mean of zero and the vertical scale is in S D units.

spheric pressure) for 1955-59 is shown in Figure 7.                   and perhaps with an anomalous weakening of the
Differences greater than 58 cm are believed to                        trade winds of the southern hemisphere and a
indicate a stronger than normal flow and differ-                      concurrent reduction of equatorial upwelling
ences less than 58 cm a less than normal flow. It                     t Bjerknes 1966; Favorite and McLain 1973).
can be seen that the period of less than normal                          Wickett 1967) found a relationship between
flow in 1957-58 corresponds well with the timing                      the year-to-year changes in zooplankton volume
of the increase in temperature in the southern                        for the CalCOFI survey (Thrailkill 1963) and the
California offshore zone. In the California Cur-                      mean meridional E k m a n transport (Fofonoff
rent region, and indeed over most of the eastern                       1962) for January t o August in the previous year
North Pacific, the increase in temperature per-                       a t l a t . 50"N. long. 140"W ( o v e r 1,000 miles
sisted through 1958 and 1959 while the sea level                      upstream from the CalCOFI survey area) for the
differences indicate a normal or above average                        years 1952-59. He suggested t h a t a major cause of
flow during this time. The period of below normal                     variation in the abundance of zooplankton in the
flow corresponds with El Nirio off the coast of Peru                  California Current region is the change in the
364
COLEBROOK: FLUCTUATIONS IiX BIOMASS OF ZOOPLANKTON




                                                                                                              < 15'
                                                                                                              15°-17'

                                                                                                              > 170




                                                                                                         FIGL~RE   7.-Topi A contoured diagram
                                                                                                         of monthly vertical t e m p e r a t u r e
                                                                                                         profiles for the upper 50 m for the years
                                                                                                         1955.59 for t h e southern California
                                                                                                         ofTshore zone (see Fikxre 1 . CalCOFl
                                                                                                                                      1
                                                                                              \t.        survey data. Bottomi .\ graph of the dif-
                                                                                                         ference in sea level hetween Honolulu
                                                                                                         and San Francisco a t nionthly intervals
                                                                                                         for the years 1955-59I plotted from Saur
                                                                                                         19721.
4
w
             1955
                        1       1956
                                          1       1957
                                                             I       1958
                                                                               I
                                                                                       1959
                                                                                                   I
v)




proportion of t h e superficial wind-driven water                           of t h e common pattern a m o n g t h e components is
t h a t is swept southward out of t h e North Pacific                       perhaps not surprising. Figure 9 shows t h e s a m e
subarctic circulation.                                                      for each taxonomic category; again t h e majority
    There seems little doubt t h a t t h e change in                        a r e second components a n d only one, for Radio-
temperature in 1957 a n d its persistence through                           laria, is t h e fourth component. T h e main features
1958 a n d 1959 is related to t h e relative reduction                      of t h e pattern are a low in 1957 a n d highs in 1956
in biomass of t h e zooplankton associated with t h e                       a n d 1958: 1955 a n d 1959 tend t o be low but their
first principal components of all zones and most of                         positions vary soniekvhat within both t h e zones
t h e taxonomic categories. T h e d a t a presented by                      and t h e taxonomic categories.
Wickett showed a marked reduction in southward                                   Coastal upwelling is ii feature of t h e Calif'ornia
transport a t lat. 50 N , long. 140"W during 1958                           C u t w n t region. a n d Bnkun (1'3731 h a s produced
a n d 1959 a n d this, coupled with t h e reduction in                      estimates of t.elative fluctuations in upwelling a t a
t h e flow of t h e California C u r r e n t i n 1957 a n d                 number of positions along t h e west coast of North
1958 (Figure 7), would appear to support Wick-                              America. T h e y a r e bnsed on e s t i m a t e s of t h e
ett's suggestion of a direct influence by water                             offkhore component o f t h e E k m a n transport which
movements. T h e relationship hctwecn t h e north                                i n t u r n estimated from atmospheric pressure
to south geographical gradient ~Figiirc, 1and the           3                    Ids.
first principal components is also cwtit.chly con-                               M o n t h l y m w n s of t h e upwelling index for five
sistent with this hypothesis.                                               positions off' thc coast at Iatitiidc> a n d longitude
    An examination of' t h e remaining components                           36 N. I 2 2 W; 3 3 ~ N .119 W: 30 N. 116 W: 27 N.
for each of t h e zones indicated t h c existence of' il                     116 W; a n d 24"N. 1l:j'W. Ihi. t h e pcriod 1955-58
second pattern of fluctuation coninion to most of'                          were extracted f'roni Rnkun's tvpott. LJncertain-
t h e zones. In Figure 8 are given g r a p h s of' a                        t i e s ;I bout t h e ci i ffe r e n ces i t i a hso 1u t c b t c i ' n i s
component, other t h a n t h e first, for each zone                         he t w c'e n t h e e s t i in u t e s a t d i t'fer e t i t pos i ti on s
selected to give t h e best approximation t o a form                        particularly off southcrn C'aiifi)tmia. discussed by
common to all t h e zones. In 8 of t h e 14 zones it is                     B a k u t i , s u gg t ed t h a t p r i n c i p R I co ti1 pone n t s
                                                                                                 c b s


t h e second component; in t h e remaining zones it is                      might provide a good method of summarizing t h e
either the third or t h e fourth component. Given                           d a t a f ' h m this set of positions. For each calendar
t h e q u a n t i t y a n d t h e quality of t h e original d a t a         month. analyses were cariicd out on t h e index
a n d c o n s i d e r i n g t h e l a r g e p r o p o r t i o n of t h e    e s t i m a t e s for t h e five positions a n d t h e 5 yr.
variability of t h e d a t a associated with t h e first                    Examination of t h e components showed t h a t a
components. t h e lack of consistency in t h e position                     pattern common to t h e first 7 mo of t h e year was
                                                                                                                                                 365
                            C C A L OF        C C A L iN
                                          I



T31
+2

'I
,      :,,
        CAL

          ~   ;
                  sw
                  ".,   I.
                         :
                           r:
                        I;cAL      cF             cAL i N




-'I '
-?
                                \.
-3b
      B C A L SW            B C A L OF,       B C A L 'b        B C A L BAY
                        I                 I                 I
C

                        I
-3-
*31 S , d J       SW    is                    S   BAJ   Y   5556575859        -3       OSTR
                                                                                                    I PTER   9     I
                                                                                                                       RADL
+2




-3-                                                                           -3-       b

                                                                              -3 T H A L            55 56 57 58 59 55 56 57 58 59 55 56 57 58 59
                                          c   CAPE "                           -I
                                                                              -:




                                                                              -1
                                                                              -2
                                                                              -3   -
                                                                                         '.
                                                                                   55 56 57 58 59
                                                                                                         YEAR




present \vithin t h e components. nnd graphs nf                               involved. X Z tth t h e first component i n relation
t h t w are given in Figure 10. The pattei'n \\.:is                           to t h e t e m p e r a t u r e range. t h e precise mecha-
tnund ,is t h e first component i n all t h e month-                          nisms involved cannot be inferred from t h e infor-
except March a n d .April \ \ h e r e i t \v:i? found i n t h e               mation here. Vp\velling h n s effects on t h e vertical
+econd component. Graphs o f t h e first component.<                          ttaniperature s t r u c t u r e anti particularly uti t h e
t'or .August to Decemtwr are .ilso $\-en in Figure                            timing of t h e t..tahli.;hinent of' a clear thermo-
10                                                                            cline. I t can i i l - t ~ be espected to have a cnn..idc~-
   T h e r e i.; u ninrked similai.it>- bettveen t h e                        able influence on t h e suppl!- of nuti'ient.G. It I -
pat t c r ti of yea r-t o -year flu c t u :it i n tis i 11 u p ive 1 I i ng   protxible. therefore. t h a t t h e effect on t h e zoo-
as represented by t h e components for t h e first 7 in0                      plankton i - a n indirect one through t h e influence
ot'each year a n d t h e fluctuation? i n tiionla-s of t h e                  of vertical stability of t h e \vater c o l u m n and the
z 00 p 1a n k t o n r e p r e se ti t ta d by t h e c n m po n e n t i        supply of nutrients on primary production pro-
sh0Lr.n in Fipurt.s P a n d 9. iind it is reasonable t n                      cesses. Peterson 119731h a s established a relntion-
assume t h a t some form nf cnu-a1 relation5hip is                            . h i p bet tve t.t i >.e r-t o->-ea v a r i ;it i on i n u p\ve 11i n g
                                                                              <                       a          r
366
COLEBROOK FLUCTUATIONS IN BIOMASS OF ZOOPLANKTON

                                                                 The precise mechanisms involved are not clear,
                                                                 but in relation to the California Current there is a
                                                                 similarity in the relationships within the taxa
                                                                 with respect to both geographical distribution and
                                                                 annual fluctuations in abundance which suggests
                                                                 t h a t advection of stocks may be involved to a
                                                                 considerable extent. The influence of upwelling on
                                                                 primary production through effects on tempera-
                                                                 ture stratification and t h e supply of nutrients
                                                                 probably accounts for the relationship with the
                                                                 zooplankton.
                                                                     The only data t h a t have been produced rou-
                                                                 tinely from the whole series of CalCOFI cruises,
                                                                 which relate to plankton other t h a n fish eggs and
                                                                 larvae, are in the form of displacement volumes of
                                                                 unsorted samples ( S m i t h 1971). The m a r k e d
+2                                                               coherence between the various taxonomic cate-
+ I
                                                                 gories suggests that these data can be expected to
                                                                 produce estimates of long-term variations which
                                                                 indicate real changes in the abundance of the
-I
                                                                 zooplankton. Such data cannot. however, reflect
                                                                 the geographical differentiation within the zoo-
                                                                 plankton, and this imposes a limit, to the extent to
                                                                 which they can be used, to provide the basis for the
                                                                 examination of the influences of a complex of
                                                                 environmental factors of the kind suggested by
                                                                 t h i s s t u d y a s p l a y i n g a n i m p o r t a n t role in
                                                                 determining the year-to-year fluctuations in the
                                                                 plankton.
- d -
                                                                     The taxonomic categories used in this study
      55 56 57 58 59 55 56 57 58 59 55 56 57 58 59               were selected by Isaacs e t al. ( 1969) to represent
                                                                 the plankton as food for fish. I have used them to
                          YEAR
                                                                 represent fluctuations in the zooplankton as such
FIGI~RE  10.-Graphs of principal components of upwelling index   for the 1955-59 period.
for the CalCOFI survey area for each month for the years 1955-       For future studies the only definitive method of
59. See text and Bakun 119731.
                                                                 selecting taxa to represent year-to-year changes
off t h e coast of Oregon and the catch of t h e                 in the zooplankton is by trial and error: there are,
Dungeness crab, Cnuccr magister-. with a time lag                moreover, numerous possibilities, and the labor
of about 18 mo. He attributed this t o a n increased             involved would be prohibitive if some compromise
food supply in years with pronounced upwelling,                  is not made. It is indicated above that there is a
implying a relationship between upwelling and                    tendency for taxa which have similar geograph-
plankton similar in sign to t h a t found further                ical distributions also to show similar year-to-
south in the California Current.                                 year fluctuations in abundance. As a first approxi-
                                                                 mation, this fact might be used as a guide to the
                    CONCLUSIONS                                  selection ofrepresentative categories. It is implicit
                                                                 that each selected category should be geographi-
  At least during the period 1955-59, a consider-                cally homogeneous, and the set of categories should
able proportion of the variability from year to year             cover the full range of geographical distributions.
in the biomass of zooplankton, as represented by                     It is probable that the species is the highest
estimates for the taxa listed in Table 1, can be                 taxon for which geographical homogeneity can be
associated with hydrographic events, variations                  assumed, and even here there may be some species
in the strength of the California Current, and                   which have geographically differentiated races.
variations in the intensity of coastal upwelling.                Isaacs et al. (1969)gave a n estimate of about 550
367
                                                                                                   FISHERY BULLETIN: VOL. 75. NO. 2

species found, or likely t o be found, i n t h e                            negative anomalies of sea surface temperature, 1953-
                                                                            60. Nature tlond.) 244:139-143.
zooplankton of the CalCOFI survey area. Allow-
                                                                    FLEMINGER.     A.
ing for the fact t h a t somewhere between one-half                      1964. Distributional atlas of calanoid copepods in the
and three-quarters of these species will probably                           California Current region, Part 1. Calif. Coop. Oceanic
occur infrequently in samples, the labor involved                           Fish. Invest. Atlas 2.313 p.
in routinely analyzing for this number of species is                FLEMINGER. J. D. ISAACS. .\ND J. G. WYLLlE
                                                                                   A,.
                                                                         1974. Zooplankton biomass measurements from CalCOFI
very considerable. The geographical distributions                           Cruises of July 1955 to 1959 and remarks on comparison
of species belonging to many of the major taxa                              with results from October, January and April cruises of
within the zooplankton have been studied and                                1955 to 1959. Calif. Coop. Oceanic Fish Invest. Atlas 21,
published in t h e CalCOFI Atlas series which                               118 p.
                                                                    F ~ F O N O F F .P.
                                                                                  N.
could provide t h e basis for t h e selection of a
                                                                         1962. Machine computations of mass transport in the
limited number of species which will represent the                          North Pacific Ocean. J. Fish. Res. Board Can. 191121-
range of geographical distributions in tile survey                          1141.
area and, hopefully, will provide a good represen-                  IsA,\c.S. J. D., A. FI.EMIN(;EII A N I ) J. K. MIILER.
tation of the range of year-to-year fluctuations in                      1969. Distributional atlas of zooplankton biomass in the
                                                                            California Current region: spring and fall 1955-1959.
abundance.                                                                  Calif. Coop. Oceanic Fish. Invest. Atlas 10, 252 p.
                                                                         1971. Distributional atlas of zooplankton biomass in the
              ACKNOWLEDGMENTS                                               California Current region: winter 1955-1959. Calif.
                                                                            Coop. Oceanic Fish. Invcst. Atlas 14. 122 p.
  My t h a n k s a r e d u e t o B r i a n Rothschild.                       M.
                                                                    KENI)AI,I.. G.
                                                                         1957. Acourseon multivariate analysis. CharlesGriffin.
Director, Southwest Fisheries Center. National                              Lond.. 136 p.
Marine Fisheries Service, NOAA, for making                          LOS(;II~'IWI'. R.
                                                                                    A.
available to me the facilities of the La Jolla                           1967. The pelagic phase of' P/c,irr.~iri~.,,dc.,sl n t i i p c s
                                                                                                                               p
Laboratory. I also thank J . D. Isaacs for furiiish-                        Stimpson tCrustacea. Galatheidne) in the California Cur-
                                                                            rent. Calif. Coop. Oceanic Fish. Invest. I h p . 11:142-154.
ing unpublished data. Nancy Wiley and Dorothy                       M , G o \ v 1s. A.
                                                                                   J.
Roll were of great assistance in the computations                        1971 Oceanic biogeography of the Pacific. Irr B. M. Fun-
involved in the study and John G. Wyllie helped                             nel and W. R. Riedel (editors),The micropaleontology of
with some data problems. Finally I must thank                               oceans, p. 3-74. Cambridge Univ. Press.
Paul E. Smith whose knowledge of the California
                                                                           1957. The marine research committee, 1947-55. Calif.
Current region and of the CalCOFI survey was                                 Coop. Oceanic Fish. Invest. Prog. Rep. 1953-1955. p. 7-9.
invaluable. My visit to the La Jolla Laboratory                     PP:'I'ICKS~!V. T. N'
was supported by the U.K. Natural Environment                              1973. Upwelling indices and annual catches of Dungeness
Research Council.                                                            crab, Cancer ningisk.r.. d o n g the west coast of the United
                                                                             States. Fish. Rull.. U S . 71:902-910.
                                                                              .
                                                                    S \ [ ' HJ. F. T.
               LITERATURE CITED                                            1972. Monthly sea level differences between the Hawaiian
                                                                             Islands and the California coast. Fish. Bull.. U.S.
AfllS'I'H0.21. E. 14.                                                        70:619-636.
      1954. Distribution and abundance of egg and larval popu-      SI.:'rTI< 0 . E.. A N I ) J. D. ISi\ACS iE1)ITOKSI
           lations of the Pacific sardine. U.S.Fish Wildl. Serv..          1960. Part 11. Symposium on the changing Pacific Ocean in
          Fish. Bull. 56:83-140.                                             19.57 and 1958. Calif. Coop. Oceanic Fish. Invest. Rep.
B A K I ' N . A.                                                             7:13-217.
      1973. Coastal upwelling indices, west coast of North          Sairrti. P. E.
           America, 1946-71. U S . Dep. Commer.. NOAA Tech.                1971. Distributional atlas of zooplankton volume in the
           Rep. NMFS SSRF-671, 103 p.                                        California Current region. 1951 through 1966. Calif.
BJEKKNES. J.                                                                 Coop. Oceanic Fish. Invest. Atlas 13, 144 p.
      1966. Survey of El Ninn 1957-58 in its relation to tropical                       II I.
                                                                    T I I H A I I . I ~ J. .R. .
          Pacific meteorology. IIn Engl. and Span. I Inter-Am.             1963. Zooplankton volumes off t h e Pacific coast,
          Trop. Tuna Comm. Bull. 12:25-86.                                   1959. U.S. Fish Wildl. Serv., Spec. Sci. Rep. Fish. 414,
BRIN'TON. E .                                                                77 p.
      1962. The distribution of Pacific euphausiids. Bull.                      w. P.
                                                                    wll'l<l~:'1"l'.
          Scripps Inst. Oceanogr.. IJniv. Calif. 8:51-270.               1967. Ekman transport and zooplankton concentration in
FAVOKITE. F., ANI) D. R. MC'LAIN                                           the North Pacific Ocean. J. Fish. Res. Board Can.
     1973. Coherence in transpacific movements ofpositive and              24:581-594.




368